Offshore natural-gas production from methane-hydrate (MH) reservoirs has received considerable attention. In this study, the offshore production method is briefly described, followed by the flow loop experiments performed to investigate the formation processes of MH in methane-in-water bubbly flows. Transient processes of phase transformation are characterized by phase paths, flow morphologies, pump heads, and in-situ particle-size measurements. It is realized that an MH slurry is generated by MH shells covering unconverted bubbles, whereas it can be transformed into a colloidal flow with fine crystalline particles under an intense turbulent shear. This study suggests that, in practice, the flow pattern under MH formation would be determined by the phase path and the flow velocity in the pipeline, which is one of the important factors considered in the evaluation of flow-assurance risks.

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